Electronic components of various types are used throughout the electronics industry. Such devices typically include DIPs, PLCCs, and SOICs. Such components are assembled into printed circuits by placing them at defined locations on a host structure, such as a printed circuit board, the locations depending upon the functions of the devices, the architecture of the circuits, etc.
Because many of these devices, typically, are needed to assemble a circuit board, means to handle such a multiplicity of components quickly and accurately is important. Additionally, a reliable handling mechanism is necessary because of the criticality of positional placement.
The characteristics of such electronic components require the use of precision and soft-handling instruments for use in circuit assembly. In the past, various types of devices have been employed to effect this function. One type of structure which the prior art has defined as an effective mechanism for accomplishing placement is one wherein a vacuum head "holds" the component to a placement tip by the application of a vacuum, at the tip, to the component. Such an apparatus utilizes a hollow probe such as a straw-type device for picking up and placing the component to be mounted.
Once the component has been maneuvered to a location at which it is ultimately intended to be affixed, the head can be employed to maintain the component in position during affixation or can be withdrawn after placement but before permanent affixation. The typical method of attachment involves soldering of leads of the integrated circuit or other component to counterpart connections on the host structure.
A vacuum head as previously described functions to effect soft handling and adequate retention of an electronic component prior to affixation. Other problems yet exist, however, with regard to the accurate placement of a component for circuit assembly. For example, while the placement head might be properly maneuvered to effect accurate positioning of a component being handled, a pick-up mechanism typically operates, assuming that the component being handled is centered with respect to a central longitudinal axis of the head, along two axes defining the surface to which the component is to be mounted. If the component is not properly centered, of course, the leads of the component may not engage pads on the board to which they are intended to correspond. Consequently, the assembled board of which the component becomes a part may be defective. Significant dollars and man-hours can, thereby, be wasted.
Various types of structures have been designed to alleviate this problem. For example, U.S. Pat. No. 4,135,630, which issued on Jan. 23, 1979, offers one possible solution. The device of that patent utilizes the channeling of a vacuum through a hollow spindle tip for holding the chip component after its selection from storage. A centering mechanism is employed to locate the chip centrally on the pick-and-place spindle. The X locators and Y locators comprise pairs of opposed centering arms. The centering arms are pivoted at a location axially spaced from the location at which the arms engage the electronic component being centered. The engagement portions of the arms, therefore, move through an arcuate path.
A similar structure is taught by U.S. Pat. No. 4,527,327. That patent issued on July 9, 1985 for a structure entitled DEVICE FOR TRANSFERRING AN ELECTRIC OR ELECTRONIC COMPONENT TO A MOUNTING BOARD. The device of that patent employs gripping means having two pairs of jaws for aligning and centering the component. Again, as in the '630 patent, the jaw arms are pivotally mounted and swing downwardly as they are pivoted inwardly to effect the centering function.
As will be able to be seen, as the centering arms move inwardly to effect centering, they have an apparent axial movement because of the arcuate path they follow. Consequently, the jaws could conceivably "miss" the component they were intended to center if the component has a dimension along the axis along which the jaws center the component which is sufficiently great.
The measure of arcuity of the path will, of course, be diminished the longer are the jaw arms. Space limitations would, however, dictate that some limitation be placed upon their length. As a result, the arcuity of the path of the end of the jaw arms can be relatively significant.
Another solution which the prior art has proposed is one embodied in a structure such as that illustrated in U.S. Pat. No. 4,174,847. That patent issued on Nov. 20, 1979 for a device entitled PRECISION CENTERING DEVICE. The device of that patent utilizes a pair of relatively moveable plates which form a guideway for four relatively moveable guides. A tapered centering port having a rectangular profile is formed by the guides. The guides are constrained for mutual coacting movement by the plates.
The relative positions of the moveable plates define the geometric shape of the centering port, and the relative locations of the guides determine the size of the centering port. The structure of the patent employs an adjusting member which operates a guide positioning device. As the adjusting member is turned, the plates slide along the face of an opening to adjust the size of the centering port.
While this structure does not have the drawbacks of those of the two previously discussed patents, it certainly has some shortcomings. For example, while a centering mechanism is typically limited to a maximum size in an axial direction along the axis of the pick-and-place spindle, size limits dictated also bear upon the maximum dimension radially with respect to that same axis that the device can have. The device of the '847 patent, in view of its method of functioning, would typically have a relatively significant radial dimension. That dimension might be one exceeding maximum available dimensional parameters.
It is to these problems of the prior art and the advantages that solutions to these problems would provide that the present invention is directed. It is a centering mechanism which not only is accurate, reliable, and efficient, but it is also one which enables streamlining and maximizing space utilization.